Vanadium and molybdenum disorder in M_(2.5)VMoO_8 (M = Mg, Mn, and Zn) determined with neutron powder diffraction and phase formation studies of Mg_(2.5+x)V_(1+2x)Mo_(1-2x)-O_8

摘要

Disorder between the vanadium and molybdenum sites was investigated using neutron diffraction on polycrystalline samples of M_(2.5)VMoO_8 (M = Mg~(2+), Mn~(2+), Zn~(2+)) and the distribution of V~(5+) and Mo~(6+) among the tetrahedral sites was determined to be nearly statistical. The refined structures for all three polycrystalline samples corroborate those of corresponding single crystals determined previously with X-ray single crystal diffraction. Studies directed at the formation of Mg_(2.5+x)V_(1+2x)Mo_(1-2x)O_8 (x = 0, + -0.02 and + -0.04) demonstrate that the phase begins to form at an appreciable rate at 1173 K, which is approximately 250 K below its melting point.